SAN FRANCISCO, Feb. 15 (UPI) — Experts say they are at a loss to explain why at least 1,000 brown pelicans died or were placed in danger in recent weeks along the California coast.

The San Jose (Calif.) Mercury News said Monday pelicans have been found dead or in distress on beaches from San Francisco to San Diego during the past month

“It’s a mystery. It’s tragic. It’s very sad to see these poor birds suffer,” California Department of Fish and Game spokeswoman Dana Michaels said. “I hope we can get to the bottom of it. There’s something really endearing about pelicans.”

Many brown pelicans found alive on beaches were disoriented and hungry with their feathers coated in a mysterious substance, officials said.

The substance, which could be from a variety of ocean conditions, limits the insulation properties of the pelicans’ feathers, putting the birds at risk for hypothermia in cold waters.

Jay Holcomb, director of the International Bird Rescue Research Center in Cordelia, Calif., told the Mercury News the substance can be cleaned off and most of the rescued pelicans can eventually return safely to coastal waters.